FIG. 7 shows the configuration of an image data transfer system comprising a digital camera and external devices according to the prior art (see JP-A-2002-271721).
The image data transfer system 700 comprises a digital camera 710, as well as a personal computer 720, a printer A 730, and a printer B 740 serving as external devices. The printer A 730 and the printer B 740 have a processing capability of acquiring image data from the digital camera 710 and then printing the image. In the image data transfer system 700, each of the digital camera 710, the personal computer 720, the printer A 730, and the printer B 740 has an interface which supports a USB (universal serial bus). The digital camera 710 is USB-connected to the external devices respectively through USB cables 750a-750c. 
As for the external devices connected to the digital camera 710, the printer A 730 or the printer B 740 can acquire and directly print out image data which has been image-acquired and recorded in the inside of the digital camera 710. The personal computer 720 can delete the image data stored in the digital camera 710. As such, various kinds of processing for the image data stored in the digital camera 710 can be performed under the control of the external devices.
Meanwhile, devices capable of USB connection can have a plurality of communication modes. When communication partners have the same communication mode, their communication is achieved so that data transfer or the like can be performed.
In the image data transfer system 700, the printer A 730 is a mass-storage class supporting device which recognizes the digital camera 710 as a mass storage device, and has a communication mode corresponding to the mass storage class. The printer B 740 is an imaging class supporting device which recognizes the digital camera as an imaging device, and has a communication mode corresponding to the imaging class. The personal computer 720 has communication modes corresponding to both classes described above. The personal computer 720 can recognize the digital camera as a mass storage device as well as an imaging device, and has two communication modes corresponding to the mass storage class and the imaging class.
These external devices try to perform communication necessary for image data transfer, on the assumption that a device serving as the partner in the USB connection has the same communication mode as their own communication mode. Nevertheless, communication is not achieved when the partner device does not have the same communication mode.
In the use of such external devices, a user of the digital camera 710 selects in advance any communication mode from the group consisting of the mass storage class and the imaging class in correspondence to the class of an external device to be connected, so that the set up is achieved such that the communication mode becomes the same as that of the external device.
This allows the digital camera to support external devices in both cases that an external device like the printer A 730 recognizes the digital camera as a mass storage device and that an external device recognizes the digital camera as an imaging device although not shown in the figure. This allows the digital camera 710 to be connected to various external devices.
Nevertheless, in order to select a communication mode, the user needs to understand the communication modes in both of the external device and the digital camera 710, and find what kind of a communication mode is used in the present system, so as to select and set an appropriate communication mode of the digital camera 710. This has been a notably annoying work for users, and has caused inconvenience especially to users unfamiliar with the operation of the digital camera 710.